I first came across the term deadnaming quite recently, which might seem quite odd for someone who doesn't use the same name as they were given when a child (I don't) but firstly in my family selecting a different name in teenage years is common practice (all part of growing up - every one of my sisters made a similar transition) and secondly pretty much nobody calls me by my childhood name, largely because I don't have any friends I'm in regular contact with who also knew me as a child.
It may also have something to do with the fact that when I changed my name from a gender neutral to a gender inappropriate name, I was making a statement about gender, but not one of conformity. It was more a statement of anti-gender, an acknowledgement of disruptive nature, like punk clothes, tattoos, or too many piercings. In that, I was just part of a general loosening of cultural norms, and accepting my name went alongside all of those other things.
But in recent years, there has been a growing trend for marketing emails from companies of which I am a customer to address me by first name. This has been followed by online systems of which I am a listed user (online administration systems, moodles, etc.) starting to do the same. The vagaries of registration systems means that sometimes I can use my initials, but sometimes that won't validate. My documentation (and indeed some of these systems) include my used name, but most places which address you by name draw from the master First Name field, not preferred first name.
So it is that there is a constant dip dip drip of automated systems addressing me by a name I don't use. It's dislocating, irritating and occasionally distressing, if it catches me at low ebb, like a reminder of old battles I don't want to fight again. In particular one provider of services, who uses a friendly chummy tone and FIRST NAME IN CAPITALS in the email headers of all its contacts with me (which really does make it look like spam or scam) has me pretty much constantly annoyed with them (it is a company that seems to derive a certain satisfaction from dissatisfied customers).
Complaining and correcting can sometimes be done (although it's not practical and sometimes not possible within some systems, and hard to predict which it will be before you start the process). But fundamentally, I don't want to be an exception. In this world, there are names people are called, and suggesting they do things using those names often makes those things more likely to be done. Acknowledged. There are also the names on their passports, Doctor's records and birth certificates. These are often not the same, for many people. The changes can be big or small, but we hear them. We hear them all.
Don't cross the beams. If you're talking formally, keep it formal and and keep FIRST NAME down in official spaces (For the Attention of: X, Dear X, According to our records your name is X). If you're striking an informal note (Hi X, Hello X!) make sure that field is draws from a preferred name field or is user editable. Otherwise that name will have precisely the opposite effect to the intended.